Color separation and synthesis systems, color separation systems and color synthesis systems, illumination optical systems, projection optical systems, and projection display devices using these systems

ABSTRACT

Color separation and synthesis systems, color separation systems and color synthesis systems, illumination optical systems, projection optical systems, and projection display devices using these systems include a wavelength-splitting element that reflects linearly polarized light of one wavelength and transmits light of another wavelength; a polarization-transforming element that changes the direction of polarization of linearly polarized light of one wavelength and that is arranged adjacent and at least nearly parallel to the wavelength-splitting element; and a polarization-sensitive beam splitter that reflects light having one direction of linear polarization and transmits light with another linear polarization. These systems provide for dividing rind combining three linearly polarized light beams of different wavelengths so that they provide imaging beams to and from display elements, such as LCOSs, that can produce a high quality full color image with fewer optical elements in the various systems and the projection display device.

This is a divisional application of allowed U.S. application Ser. No.10/954,185 filed Oct. 1, 2002 now U.S. Pat. No. 7,220,002, the benefitof priority of which is hereby claimed under 35 U.S.C. 120.

FIELD OF THE INVENTION

The present invention relates to separation and/or synthesis systems oflight beams according to polarization and wavelength characteristics ofthe light beams. Additionally, the present invention relates toprojection display devices that use such systems in their illuminationoptical systems and/or their projection optical systems and that uselight beams that are modulated with image information by displayelements for magnified projection, and especially relates to suchprojection display devices that use reflection-type display elementswith polarization changing properties, such as some liquid crystaldisplay elements.

BACKGROUND OF THE INVENTION

In recent years, the projector market has been growing rapidly, alongwith the use of personal computers. Liquid crystal display elements ofthe transmission-type and the reflection-type, and DMD display elementswhich include micromirrors in an orderly array, are known as lightvalves that modulate light in order to produce image light signals. Inparticular, an image display device of the reflection-type is suitableto create very small picture elements with high efficiency, andtherefore it has gained attention as an image display device forproducing a high quality image.

Various projection display devices have been developed that usereflection-type display elements and polarization properties of lightbeams. For instance, projection display devices that illuminatereflection-type display elements with polarization changes after colorseparation of the light beams according to wavelengths from a lightsource by an illumination optical system with a projection opticalsystem that use four polarization-sensitive beam splitters, generallyknown as a COLORQUAD™, and that project imaging light beams from thereflection-type display elements, are known. FIG. 26 and FIG. 27 arecross-sectional diagrams of prior art Example 1 and prior art Example 2of such devices. In FIG. 26 and FIG. 27, light beam channelscorresponding to each of the three primary colors of light are shown asstraight lines, and short intersecting lines and the black round shapesshown on these lines indicating the paths of the three light beamsindicate one of two polarization states (S polarized light or Ppolarized light) of each of the light beams at particular locations inthe projection display devices. In the following descriptions, the shortintersecting lines are called the first polarization state and the blackround shapes are called the second polarization state of the lightbeams.

Light from a light source (not shown), enters from the bottom as shownin FIG. 26 and FIG. 27 (into COLORQUAD™ 159 as shown in FIG. 26) asthree different colors with their polarization states adjusted to be thesame(the first polarization state). The light is separated into lightbeams of the three primary colors in the color quad 159. The light beamsare modulated by the three reflection-type, liquid crystal panels 153 a,153 b, and 153 c, in particular LCOS (Liquid Crystal On Silicon), thatare reflection-type display elements with polarization properties formodulating the light beams of the three primary colors with imageinformation. A light beam that contains the image information of allthree colors is synthesized and emitted from the COLORQUAD™, projectedby the projection optical system 162 d, and a full color image is formedon a screen (not shown). Each of the three different light paths shownin FIG. 26 may correspond to any one of the three primary colors blue,green and red in the following description of the operation of theCOLORQUAD™ 159.

As shown in FIG. 26, in the COLORQUAD™ 159, four polarization-sensitivebeam splitters (which term may hereinafter be abbreviated as PBSs) 170a, 150 a, 150 b, and 160 a are arranged so that their internalpolarization-sensitive filters 171, 151 a, 151 b, and 161, respectively,are aligned in the shape of the letter X. The first PBS is anillumination light beam separation element 170 a; the second PBS is anoptical path separation element 150 a; the third PBS is an optical pathseparation element 150 b; and the fourth PBS is a projection light beamsynthesis element 160 a. The COLORQUAD™ 159 includes first through thirdLCOS, 153 a, 153 b, and 153 c, first through fourth wavelength-specific,polarization-transforming elements 143 a, 143 b, 143 c, and 143 d, firstthrough third polarizing plates 142 a, 142 b, and 142 c, andquarter-wave plates 152 a, 152 b, and 152 c. Furthermore, in order toimprove contrast of the projected image, the following arrangements aremade: the polarizing plate 142 a adjusts the polarization direction ofan incident illumination light beam to the first polarization state; thepolarizing plate 142 b adjusts the polarization direction of the secondcolor light beam which is incident thereon to the second polarizationstate; and the polarizing plate 142 c adjusts the polarization directionof a projection light beam to the second polarization state.Furthermore, the wavelength-specific, polarization-transforming elements143 a, 143 b, and 143 d are elements for rotating the direction oflinear polarization a specified angle. The wavelength-specific,polarization-transforming elements 143 a and 143 d transform the secondcolor light beam to the second polarization state from the firstpolarization state, and the wavelength-specific,polarization-transforming elements 143 b and 143 c transform the firstcolor light beam to the second polarization state from the firstpolarization state.

Illumination light beam separation element 170 a receives light from thelight source (not shown) and interiorly reflects part of the light tooptical path separation element 150 b and transmits part of the light tooptical path separation element 150 a, and projection light beamsynthesis element 160 a receives light from optical path separationelements 150 a and 150 b to synthesize the light beams to form aprojection light beam.

Additionally, in order to achieve improved contrast of a projectedimage, the following arrangements are made: the polarizing plate 142 aadjusts the polarization of the light beam incident on the COLORQUAD™159 to a light beam in the first polarization state; the polarizingplate 142 b assures the direction of linear polarization of a light beamof a second color is in the second polarization state; and thepolarizing plate 142 c further adjusts the direction of linearpolarization of the light beam projected from the COLORQUAD™ 159 thatincludes all three colors is in the second polarization state.Furthermore, each of the wavelength-specific, polarization-transformingelements 143 a-143 d is designed to rotate the direction of linearpolarization of each light beam of a particular color a particularamount. The wavelength-specific, polarization-transforming elements 143a and 143 d transform the second color light beam to the secondpolarization state from the first polarization state, and thewavelength-specific, polarization-transforming elements 143 b and 143 ctransform the first color light beam to the second polarization statefrom the first polarization state.

With further reference to FIG. 26, the first color light beam isreflected within the illumination light beam separation element 170 a,transmitted by optical path separation element 150 b, and irradiates theLCOS 153 a that modulates the first color light beam. The second colorlight beam is transmitted through illumination light beam separationelement 170 a and optical path separation element 150 a and irradiatesthe LCOS 153 b that modulates the second color light beam. The thirdcolor light beam is reflected within the illumination light beamseparation element 170 a and then is reflected within the optical pathseparation element 150 b, and irradiates the LCOS 153 c that modulatesthe third color light beam.

Furthermore, the first color light beam is modulated with imageinformation for projection at the first LCOS 153 a and becomes a lightbeam of the first polarization state before it is reflected withinoptical path separation element 150 b and transmitted through projectionlight beam synthesis element 160 a for projection. The second colorlight beam is reflected as a light beam modulated with image informationat the second LCOS 153 b and becomes a light beam of the firstpolarization state before it is reflected within optical path separationelement 150 a and projection light beam synthesis element 160 a. Thethird color light beam is reflected as a light beam modulated with imageinformation at the third LCOS 153 c and becomes a light beam of thesecond polarization state before it is transmitted by optical pathseparation element 150 band projection light beam synthesis element 160a. Thus, as shown in FIG. 26, the light beams of the three differentcolors are combined as they are emitted from the COLORQUAD™ 159.

It has also been proposed to use only two PBSs in order to improve thecontrast of a projection display device while achieving lower cost,lighter weight, and improved polarization properties over a constructionwith four PBSs.

FIG. 27 shows a projection display device that uses reflection-typedisplay elements, particularly LCOS 153 a-153 c, each of which isilluminated subsequent to color separation based on wavelengths of lightfrom the illumination light sources. The projection display device ofFIG. 27 uses two PBSs in a manner similar to the projection displaydevice of FIG. 26, and light beams containing the image information fromthe three LCOS 153 a-153 c related to different wavelengths aresimilarly projected through the projection optical system 162 d. In theprojection display device of FIG. 27 a dichroic mirror 170 b initiallydivides the light beams according to color rather than a PBS such as PBS170 a of FIG. 26 that initially divides the light beams according topolarization state. Similarly, in the projection display device of FIG.27 a dichroic mirror 160 b synthesizes the light beams based onwavelength for projection rather than a PBS such as PBS 160 a thatsynthesizes the light beams according to polarization state.

In the projection display device shown in FIG. 26, a total of fourwavelength-specific, polarization-transforming elements 143 a-143 d arepresent, each of which is either in the illumination optical system(from the light source to the LCOS) or in the projection optical system(from the LCOS to the projection lens), whereas a total of only twowavelength-specific, polarization-transforming elements are arranged inthe projection display device of FIG. 27. However, the angle ofincidence properties and wavelength selective properties of thewavelength-specific, polarization-transforming elements are notnecessarily satisfactory and may be the main causes of deterioration ofcontrast and deterioration of image formation performance of theprojected image.

Concerning these problems, Japanese Laid-Open Patent Application2001-100155 describes a projection display device that uses two PBSs anddoes not include any wavelength-specific, polarization-transformingelements. In this publication, a low cost optical system that uses twoPBSs is disclosed for a projection display device that usesreflection-type, liquid crystal display elements. This optical systemprovides separation of a light beam from a light source or device intoplural light beams according to wavelengths by a first dichroic mirrorand provides a ninety degree rotation of the direction of linearpolarization of one of the separated light beams by apolarization-transforming element. This optical system also uses asecond dichroic mirror to further separate one of the previouslyseparated light beams according to wavelengths, as well as to synthesizethe other of the light beams previously separated by wavelength at thefirst dichroic mirror with one of the light beams of a differentwavelength separated according to wavelengths at the second dichroicmirror. Subsequently, the light beams of the three different wavelengthsilluminate different reflection-type, liquid crystal display elements.

The illumination optical system of this projection display deviceenables two adjacent reflection-type, liquid crystal display elements tobe illuminated with light beams of different wavelengths and differentpolarization states appropriate for operation with an adjacent PBSwithout using a wavelength-specific, polarization-transforming elementwhile making the entire device compact and decreasing the number of PBSsrequired. Two light beams having different directions of linearpolarization and different wavelengths are emitted in the same directiontoward the PBS from the second dichroic mirror that performs bothseparation and synthesis of various light beams, and th light beam ofthe other wavelength is emitted in a different direction.

However, there is a problem with this projection display device in thatthe polarization-transforming element that changes the direction oflinear polarization needs to be in relatively close proximity to thelight source (namely, in front of the second dichroic mirror), whichmakes it necessary for the polarization-transforming element to berelatively large.

Additionally, Japanese Laid-Open Patent Application 2001-100155 includesno description of the polarization element used to adjust thepolarization direction in the illumination optical system of theprojection display device described. However, in order to make aprojection display device with a projected image of satisfactorycontrast, a polarization element that adjusts the polarization directionis needed in the optical path. Due to the inability to accommodate thepolarization element in the optical path where light beams havingdifferent polarization directions are present, the polarization elementis placed in this optical system closer to the light source than thesecond dichroic mirror. However, because this position is closer to thelight source, the large size of the polarization element and thedeterioration of the polarization properties by placing the polarizationelement far from the PBSs that are adjacent the reflection-type displayelements are concerns. It is preferable that the polarization element bearranged closer to the reflection-type display elements and adjacent tothe incident side of a PBS.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to color separation and synthesis systems,color separation systems, and color synthesis systems that, throughconsiderations of the required directions of the linearly polarizedlight and wavelengths of the light beams in such systems, enable anincrease in the choices of the arrangements of the optical members andenable enhancing the degree of freedom in the design of these systems,including positioning a polarization-transforming element at a locationwhere it may be relatively small, decreasing the number ofwavelength-specific, polarization-transforming elements, and making itpossible to position a polarization element adjacent to the incidentside of a polarization-sensitive beam splitter, for instance,in anillumination optical system and a projection optical system of aprojection display device that uses reflection-type display elementswith polarization changing properties. The present invention furtherrelates to color separation and synthesis systems, color separationsystems, and color synthesis systems, as well as illumination opticalsystems and projection optical systems that they may include, systems,and projection display devices including any of such systems, that arecompact, of high contrast and with excellent color reproduction, and lowin production costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings, whichare given by way of illustration only and thus are not limitative of thepresent invention, wherein:

FIG. 1 is a cross-sectional schematic diagram of the color separationand synthesis system of Embodiment 1 of the present invention;

FIG. 2 is a cross-sectional schematic diagram of the color separationand synthesis system of Embodiment 2 of the present invention;

FIG. 3 is a cross-sectional schematic diagram of the color separationand synthesis system of Embodiment 3 of the present invention;

FIG. 4 is a cross-sectional schematic diagram of the color separationand synthesis system of Embodiment 4 of the present invention;

FIG. 5 is a cross-sectional schematic diagram of the color separationand synthesis system of Embodiment 5 of the present invention;

FIG. 6 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 6 of the present invention;

FIG. 7 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 7 of the present invention;

FIG. 8 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 8 of the present invention;

FIG. 9 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 9 of the present invention;

FIG. 10 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 10 of the present invention;

FIG. 11 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 11 of the present invention;

FIG. 12 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 12 of the present invention;

FIG. 13 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 13 of the present invention;

FIG. 14 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 14 of the present invention;

FIG. 15 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 15 of the present invention;

FIG. 16 is a cross-sectional schematic diagram of a color separation andsynthesis system of Embodiment 16 of the present invention;

FIG. 17 is a cross-sectional schematic diagram of a color separationsystem or color synthesis system of Embodiment 17 of the presentinvention;

FIG. 18 is a cross-sectional schematic diagram of a color separationsystem or color synthesis system of Embodiment 18 of the presentinvention;

FIG. 19 is a cross-sectional schematic diagram of a color separationsystem or color synthesis system of Embodiment 19 of the presentinvention;

FIG. 20 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 20 of the present invention;

FIG. 21 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 21 of the present invention;

FIG. 22 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 22 of the present invention;

FIG. 23 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 23 of the present invention;

FIG. 24 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 24 of the present invention;

FIG. 25 is a cross-sectional schematic diagram of a projection displaydevice of Embodiment 25 of the present invention;

FIG. 26 is a cross-sectional schematic diagram of a projection displaydevice of prior art Example 1;

FIG. 27 is a cross-sectional schematic diagram of a projection displaydevice of prior art Example 2; and

FIG. 28 is a cross-sectional schematic diagram of a projection displaydevice of prior art Example 3.

DETAILED DESCRIPTION

Color separation and synthesis systems, color separation systems, aswell as color synthesis systems, that relate to preferred embodiments ofillumination optical systems, projection optical systems andprojection-type display devices of the present invention that use suchsystems will be described with reference to FIGS. 1-28.

In particular, color separation and synthesis systems will first bedescribed with reference to FIGS. 1-16. More specifically, Embodiments1-4 of the color separation and synthesis systems that pertain to afirst mode of the color separation and synthesis systems will first bedescribed with reference to FIGS. 1-4, respectively, then Embodiments5-14 of the color separation and synthesis systems that pertain to asecond mode of the color separation and synthesis system will bedescribed with reference to FIGS. 5-14, respectively, and thenEmbodiments 15 and 16 of the color separation and synthesis systems thatpertain to a third mode of the color separation and synthesis systemwill be described with reference to FIGS. 15 and 16, respectively.Additionally, FIG. 20, more fully described below, is a cross-sectionalschematic diagram of a projection display device that may use colorseparation and synthesis systems of the present invention as one part ofthe illumination optical system of a projection display device. The term“systems” will be used in the following descriptions to refer generallyto the color separation and synthesis systems, color separation systems,color synthesis systems, illumination optical systems, projectionoptical system, and even to projection display devices that includethese systems, of the present invention and characteristics of thevarious embodiments of the present invention described herein extend toall the systems disclosed herein to which the embodiments describedherein are useful.

Color Separation and Synthesis Systems (Embodiments 1-16)

FIG. 1 is a cross-sectional schematic diagram of Embodiment 1 of thecolor separation and synthesis systems of the present invention. Asshown as 1 a in FIG. 1, Embodiment 1 of the color separation andsynthesis system of the present invention includes awavelength-splitting element, which is a dichroic mirror 10 a in FIG. 1,that reflects or transmits portions of an incident light beam accordingto the wavelength of the light and at least onepolarization-transforming element, which is a half-wave plate 11 a inFIG. 1, that changes the direction of polarization of linearly polarizedlight of one wavelength and that is arranged adjacent and at leastnearly parallel to the wavelength-splitting element. The phrase“arranged adjacent and at least nearly parallel” includes states of thepolarization-transforming element and the wavelength-splitting elementbeing superimposed or where they abut one another in a parallel ornearly parallel relationship. The phrase “nearly parallel” encompassesslight variations from parallelism that to at least a firstapproximation provide the same effects as an exact parallel relationshipwould provide. A small separation of the polarization-transformingelement and the wavelength-splitting element is allowed based onconsiderations of manufacture. However, the systems will tend to becometoo large if the separation is too large.

The incident light beam of FIG. 1 includes light of three differentwavelengths. In FIG. 1, as well as in FIGS. 2-25, the path of the lightbeams of each wavelength is shown schematically by straight lines withshort intersecting lines and black circles showing the alternativepolarization states, either one of the two polarization states (Spolarized light and P polarized light) of different polarizationdirection. Further, in the systems that relate to the present invention,to be described below, and in the color separation and synthesis system1 a, the light beams of the three wavelengths are preferably primarycolor light beams that are used to create a full color picture image. Inparticular, light beams of blue, red, and green can correspond in anyorder to the light beams of three different wavelengths shown in FIG. 1.

As indicated with regard to the three different wavelengths being, forexample, blue, red, and green, each light beam of a different wavelengthmay include light with a band of wavelengths that relate generally tothe same color, such as red, blue, or green and is not limited to amonochromatic light beam of only one wavelength. Similarly, as usedherein, a light beam of a first, second or third wavelength encompassesa light beam made up of a band of wavelengths that are similarlyreflected, transmitted, or have their polarization properties changed byoptical elements as described herein.

The color separation and synthesis system of Embodiment 1 is designedfor the following operation: the light beams of the first, second, andthird wavelengths are variously incident from different directions andundergo color separation and synthesis as shown in FIG. 1. Inparticular, light beams of the first and third wavelengths are emittedin the same direction linearly polarized in different directions, and alight beam of a second wavelength is emitted in a different directionfrom which light beams of the first and third wavelengths are emitted.

As shown in FIG. 1, the light beams of the first and second wavelengthsare incident from the right side of the page, and the light beam of thethird wavelength is incident from the lower side of the page. The colorseparation and synthesis system 1 a undertakes color separation of thelight beams of the first and the second wavelengths and also colorsynthesis of the light beams of the first and third wavelengths; thelight beams of the first and third wavelengths are emitted to the leftside of the page; and the light beam of the second wavelength is emittedto the upper side of the page. In other words, the dichroic mirror 10 ais set so that the light beam of the first wavelength can be transmittedand the light beams of the second and third wavelengths can bereflected.

Furthermore, the light beams of all three wavelengths are in the firstpolarization state when they are incident to the color separation andsyntheses system 1 a. Regarding the light beams that are emitted fromthe color separation and synthesis system 1 a, the light beam of thefirst wavelength is transmitted once through the half-wave plate 11 aand emitted in the second polarization state. The light beam of thesecond wavelength is emitted in the first polarization state withoutbeing transmitted through the half-wave plate 11 a. The light beam ofthe third wavelength is transmitted through and back through thehalf-wave plate so that it is emitted in the first polarization state.In particular, the polarization-transforming element of the presentinvention is designed to establish a specified optical path length sothat when transmitting the light beams that are incident at a specificangle of incidence to this element, the half-wave plate 11 a, forexample, creates a phase difference of one-half the wavelength of theincident light beam, specifically, for example, an angle of forty-fivedegrees as shown in FIG. 1.

FIGS. 2-4 show cross-sectional schematic diagrams of Embodiments 2-4 ofthe color separation and synthesis systems of the present invention,which are referenced by reference numerals 1 b-1 d in FIGS. 2-4,respectively. The arrangements of Embodiments 2-4 are clear from FIGS.2-4, respectively, and the description of Embodiment 1 above. Therefore,further detailed descriptions are omitted.

The color separation and synthesis systems 1 b-1 d are different fromthe color separation and synthesis system 1 a in at least one way withregard to transmission and reflection properties of the dichroic mirrors10 b-10 d, the arrangement of the dichroic mirrors 10 b-10 d and thehalf-wave plates 11 b-11 d, and/or the emitting directions of the lightbeams of the first, second, and third wavelengths.

However, similar operation may be achieved by having the light beams ofthe first and second wavelengths incident from different directions sothat light beams of first and third wavelengths are still emitted in thesame direction linearly polarized in different directions, and a lightof a second wavelength is still emitted in a different direction fromwhich light beams of the first and third wavelengths are emitted.

Embodiments 1-4 that relate to a first mode of the color separation andsynthesis systems of the present invention include the smallest numberof wavelength-splitting elements and polarization-transforming elements(namely, one of each, for a total of two such elements), and the lightbeams of the first, second, and third wavelengths are all incident onthe color separation and synthesis systems linearly polarized in thesame direction.

Furthermore, among the color separation and synthesis systems 1 a-1 d ofEmbodiments 1 through 4 that relate to the first mode, Embodiments 1, 3,and 4 are constructed so that a specified light beam is transmittedthrough and back through the half-wave plate 11 a, 11 c, or 11 d so thatthe specified light beam is emitted in the first polarization state,that is, with the same polarization state as the specified light beam isincident on the color separation and synthesis system. Additionally,among the color separation and synthesis systems 1 a-1 d of Embodiments1 through 4 that relate to the first mode, Embodiments 1-3 areconstructed so that at least two specified light beams incident fromdifferent directions are transmitted through the hall-wave plate 11 a,11 b, or 11 c to be emitted in the same direction and with differentpolarization states, as shown with regard to light beams of the firstand third wavelengths of Embodiment 1. These constructions effectivelyenable reducing the number of optical elements and increase the degreesof freedom in designing illumination optical systems and projectiondisplay devices.

Embodiments 5-14 of the color separation and synthesis systems thatpertain to a second mode of the color separation and synthesis systemswill now be described with reference to FIGS. 5-14, respectively.

As shown as 2 a in FIG. 5, Embodiment 5 of the color separation andsynthesis systems of the present invention includes: awavelength-splitting element, which is a dichroic mirror 10 e in FIG. 5,that reflects and transmits portions of an incident light beam accordingto the wavelength of the light; at least one polarization-transformingelement, which is a half-wave plate 11 e in FIG. 5, that changes thedirection of polarization of linearly polarized light of one wavelengthand that is arranged adjacent and at least nearly parallel to thewavelength-splitting element; and a polarization-sensitive beamsplitter, which is a reflection-type polarization-sensitive beamsplitter 12 a in FIG. 5, that reflects or transmits an incident lightbeam according to the direction of linear polarization of the light beamand that is arranged adjacent and at least nearly parallel to thewavelength-splitting element and the polarization-transforming element.

Similar to Embodiment 1-4 of the first mode, light beams of the first,second, and third wavelengths are variously incident on the colorseparation and synthesis systems of the second mode in differentdirections in order to undergo color separation and synthesis.Furthermore, the color separation and synthesis systems of the secondmode operate similarly to the systems of the first mode, as follows. Inparticular, light beams of the first and third wavelengths are emittedin the same direction linearly polarized in different directions, and alight beam of a second wavelength is emitted in a different directionfrom which light beams of the first and third wavelengths are emitted.

As shown in FIG. 5, the light beams of the first and second wavelengthsare incident from the right side of the page, and the light beam of thethird wavelength is incident from the lower side of the page. The colorseparation and synthesis system 2 a undertakes color separation of thelight beams of the first and the second wavelengths and also colorsynthesis of the light beams of the first and third wavelengths; thelight beams of the first and third wavelengths are emitted to the leftside of the page; and the light beam of the second wavelength is emittedto the upper side of the page. In other words, the dichroic mirror 10 eis set so that the light beams of the first and third wavelengths aretransmitted and the light beam of the second wavelength is reflected.

Furthermore, the light beams of all three wavelengths are in the secondpolarization state when they are incident onto the color separation andsynthesis system 2 a. Regarding the light beams that are emitted fromthe color separation and synthesis system 2 a, the incident light beamfrom the right side of the page of the first wavelength and secondpolarization state is transmitted by the polarization-sensitive beamsplitter 12 a, rotated by the half-wave plate 11 e to the firstpolarization state, and then is emitted by the dichroic mirror 10 e inthe first polarization state. The light beam from the right side of thepage of the second wavelength and second polarization state istransmitted through the polarization-sensitive beam splitter 12 a, ischanged to the first polarization state by the half-wave plate 11 e, isreflected by the dichroic mirror 10 e, transmits back through thehalf-wave plate 11 e, and subsequently is transmitted again through thepolarization-sensitive beam splitter 12 a and emitted in the secondpolarization state toward the top of the page. In other wolds, thepolarization-sensitive beam splitter 12 a is set so that the light beamof the second polarization state is transmitted and the light beam ofthe first polarization state is reflected.

FIGS. 6-13 are cross-sectional schematic diagrams of Embodiments 6-13 ofthe color separation and synthesis systems of the present invention,which are referenced by reference numerals 2 b-2 i in FIGS. 6-13,respectively. The arrangements of Embodiments 6-13 are clear from FIGS.6-13, respectively, and the description of Embodiment 5 above.Therefore, further detailed descriptions are omitted.

Operation of Embodiments 6-13 similar to the operation of Embodiment 5is achieved with respect to light beams of the first, second, and thirdwavelengths that are variously incident from different directions andthat undergo color separation and color synthesis. In particular, lightbeams of the first and third wavelengths are emitted in the samedirection linearly polarized in different directions, and light of asecond wavelength is emitted in a different direction from which lightbeams of the first and third wavelengths are emitted.

The color separation and synthesis systems 2 b-2 i are different fromthe color separation and synthesis system 2 a in at least one way withregard to the transmission and reflection properties of the dichroicmirrors 10 f-10 m, the arrangement of the dichroic mirrors 10 f-10 m andthe half-wave plates 11 f-11 m, the emitting directions of the lightbeams of the first, second, and third wavelengths, and/or thepolarization states of the light beams of the first, second, and thirdwavelengths at the time of incidence on the color separation andsynthesis systems 2 b-2 i.

However, similar operation may be achieved by having the light beams ofthe first and second wavelengths incident from different directions sothat light beams of the first and third wavelengths are still emitted inthe same direction linearly polarized in different directions, and alight beam of a second wavelength is still emitted in a differentdirection from which light beams of the first and third wavelengths areemitted.

Furthermore, among the color separation and synthesis systems 2 a-2 i ofEmbodiments 5-13 that relate to the second mode. Embodiments 5-10, 12,and 13 are constructed so that a specified light beam is transmittedthrough and back through the half-wave plate 11 e-11 j, 11 l, or 11 m sothat the specified light beam is emitted with the same polarizationstate as the specified light beam is incident onto the color separationand synthesis system. Additionally, among the color separation andsynthesis systems 2 a-2 i of the above Embodiments 5-13, Embodiments 5,9, 10, and 12 are constructed so that at least two specified light beamsincident from different directions are transmitted through the half-waveplate 11 e, 11 i, 11 j, or 11 l and are emitted in the same directionand with different polarization states, as shown with regard to thelight beams of the first and third wavelengths of Embodiment 5. Theseconstructions effectively enable reducing the number of optical elementsand increase the degree of freedom in designing illumination opticalsystems and projection display devices.

FIG. 14 is a cross-sectional schematic diagram of Embodiment 14 of thecolor separation and synthesis systems of the present invention. FIG. 14shows color separation and synthesis system 2 j of the second mode ofthe color separation and synthesis systems of the present invention. Thepolarization-transforming element according to the present invention isnot limited to a single half-wave plate as shown in Embodiments 1-13. Asshown in FIG. 14, Embodiment 14 includes two quarter-wave plates 13 aand 13 b as the polarization-transforming element.

In FIG. 14, the light beams of the first and second wavelengths areincident from the right side of the page and the light beam of the thirdwavelength is incident from the lower side of the page; the light beamsof the first and third wavelengths are emitted to the left side of thepage, and the light beam of the second wavelength is emitted to theupper side of the page. The dichroic mirror 10 n is set so that thelight beam of the first wavelength is transmitted and the light beam ofthe second wavelength is reflected.

Furthermore, the light beams of all three wavelengths are in the firstpolarization state when they are incident on the color separation andsynthesis system 2 j. Regarding the light beams that are emitted fromthe color separation and synthesis system 2 j, the light beam of thefirst wavelength is transmitted through the quarter-wave plates 13 a, 13b and the polarization-sensitive beam splitter 12 j in that order, andemitted in the second polarization state. The light beam of the secondwavelength is transmitted through and back through the quarter-waveplate 13 a and is emitted in the second polarization state. The lightbeam of the third wavelength is reflected at the polarization-sensitivebeam splitter 12 j and emitted in the first polarization state. This isdifferent from Embodiments 5-13 in that the color separation andsynthesis system 2 j transforms the polarization state of the light beamof the second wavelength so that it is emitted in a differentpolarization state than that in which it is incident. Thepolarization-sensitive beam splitter 12 j, similar to Embodiments 5-13,in the color separation and synthesis system 2 j of Embodiment 14 is setso that the light beam of the first polarization state is reflected andthe light beam of the second polarization state is transmitted.

Similar to Embodiments 5-13, the color separation and synthesis system 2j of Embodiment 14, which includes a plurality ofpolarization-transforming elements, operates with light beams of thefirst, second, and third wavelengths variously incident on the colorseparation and synthesis system from different directions in order toundergo color separation and synthesis. Also, light beams of the firstand third wavelengths are emitted in the same direction linearlypolarized in different directions, and a light beam of a secondwavelength is emitted in a different direction from which light beams ofthe first and third wavelengths are emitted.

A desirable feature when a plurality of polarization-transformingelements are used is that the number of times each light beam passesthrough the polarization-transforming element, such as a quarter-waveplate, should be as nearly the same as possible.

In addition, a reflection-type polarization-sensitive beam splitter isused in the second mode of the color separation and synthesis systems.Because the polarization-sensitive beam splitter operates to direct indifferent directions light beams that are linearly polarized indifferent directions, when this system is arranged as an optical systemor part of a device, there may be instances where linear polarizingfunctions may be combined with the polarization-sensitive beam splitterin order to simplify the construction of the system or device.

Color separation and synthesis systems of the second mode operate withlight beams of first, second, and third wavelengths that are linearlypolarized in the same direction and that are variously incident on thecolor separation and synthesis systems from different directions.

FIG. 15 is a cross-sectional schematic diagram of Embodiment 15 of thecolor separation and synthesis systems of the present invention thatrepresents a third mode of the color separation and synthesis systems ofthe resent invention. FIG. 15 shows color separation and synthesissystem 3 a of Embodiment 15 that includes a wavelength-splittingelement, which is a dichroic mirror 10 o in FIG. 15, and apolarization-sensitive beam splitter, which is a reflection-typepolarization sensitive beam splitter 12 k in FIG. 15, that reflects ortransmits an incident light beam depending on the direction of linearpolarization of the incident light beam and that is arranged adjacentand at least nearly parallel to the wavelength-splitting element.

Similar to the first mode of the color separation and synthesis systemsof Embodiments 1-4 described above, in this third mode the light beamsof the first, second, and third wavelengths are variously incident onthe color separation and synthesis systems from different directions.Furthermore, the color separation and synthesis system 3 a undertakescolor separation of the light beams of the first and the secondwavelengths and also color synthesis of the light beams of the first andthird wavelengths, the light beams of the first and third wavelengthsare emitted in the same direction with different polarization states,and the light beam of the second wavelength is emitted in a differentdirection.

In FIG. 15 the light beams of the first and second wavelengths areincident from the right side of the page, and the light beam of thethird wavelength is incident from the lower side of the page. The colorseparation and synthesis system 3 a undertakes color separation of thelight beams of the first and second wavelengths and also color synthesisof the light beams of the first and third wavelengths; the light beamsof the first and third wavelengths are emitted to the left side of thepage; and the light beam of the second wavelength is emitted to theupper side of the page. In other words, the dichroic mirror 10 o is setso that the light beams of the first and third wavelengths aretransmitted and the light beam of the second wavelength is reflected. Inaddition, the color separation and synthesis system 3 a is constructedso that the light beam of the third wavelength is transmitted throughand back through the dichroic mirror 10 o.

Furthermore, the light beams of the first and second wavelengths areincident on the color separation and synthesis system 3 a in the secondpolarization state, and the light beam of the third wavelength isincident on the color separation and synthesis system 3 a in the firstpolarization state. Regarding the light beams that are emitted from thecolor separation and synthesis system 3 a, the light beam of the firstwavelength is transmitted through the reflection-type, polarizationsensitive beam splitter 12 k and emitted in the second polarizationstate. The light beam of the second wavelength is transmitted throughand back through the reflection-type, polarization-sensitive beamsplitter 12 k and emitted in the second polarization state. The lightbeam of the third wavelength is reflected by the reflection-type,polarization-sensitive beam splitter 12 k and emitted in the firstpolarization state. In other words, the reflection-type,polarization-sensitive beam splitter 12 k is set so that light beams ofthe first polarization state are reflected and light beams of the secondpolarization state are transmitted.

FIG. 16 is a cross-sectional schematic diagram of Embodiment 16 of thecolor separation and synthesis system 3 b of the present invention,which, like Embodiment 15, belongs to a third mode of the colorseparation and synthesis systems of the present invention. Thearrangement of Embodiment 16 is clear from the description of Embodiment15 above. Therefore, further detailed description is omitted.

As shown in FIG. 16, the color separation and synthesis system 3 b ofEmbodiment 16 is different from the color separation and synthesissystem 3 a of Embodiment 15 (FIG. 15) in the order of arrangement of thedichroic mirror 10 p and the reflection-type polarization sensitive beamsplitter 12 l, and the dichroic mirror 10 p may be set so that the lightbeam of the first wavelength is transmitted and the light beam of thesecond wavelength is reflected. However, similar operation may beachieved by having the light beams of the first and second wavelengthsincident from different directions so that light beams of the first andthird wavelengths are still emitted in the same direction linearlypolarized in different directions, and a light beam of a secondwavelength is still emitted in a different direction from which lightbeams of the first and third wavelengths are emitted.

The color separation and synthesis systems of the third mode may beformed with the minimum number of elements, namely awavelength-splitting element and a polarization sensitive beam splitter,with light beams of first, second, and third wavelengths being variouslyincident from different directions.

Because of reflection-type polarization sensitive beam splitter isarranged as the polarization splitting plane in the color separation andsynthesis system that relates to the third mode in the same manner as inthe second mode, when this system is arranged in an optical system or ispart of a device, there may be instances where linear polarizingfunctions may be combined with the polarization sensitive beam splitterin order to simplify the construction of the system or device.

In addition, the color separation and synthesis systems of the presentinvention described above also have the ability to be used with lightpaths reversed from those shown in FIGS. 1-16, as generally taught withregard to optical elements, such as lenses. In other words, thesesystems may be used with light traveling from what is the light emittingside to the light incident side as shown in FIGS. 1-16. In thissituation, light beams of the first and third wavelengths are incidentfrom the same direction with their directions of linear polarizationbeing different, and light beams of the first and second wavelengths areemitted with the same direction of linear polarization and in adirection different from the direction in which the light beam of thethird wavelength is emitted and the light beam of the second wavelengthis incident.

Additionally, in this case, it is preferred that the light beams of thefirst, second, and third wavelengths that are emitted from the colorseparation and synthesis systems that relate to the first and the secondmodes (described above with reference to FIGS. 1-14) be emitted with thesame direction of linear polarization. Furthermore, it is preferred thatthe light beams emitted from the color separation and synthesis systemsthat relate to the third mode be such that the light beams of the firstand second wavelengths have the same direction of linear polarizationthat is different from the direction of linear polarization of the lightbeam of the third wavelength.

Color Separation Systems and Color Synthesis Systems (Embodiments 17-19)

Color separation systems and color synthesis systems that relate topreferred embodiments of illumination optical systems, projectionoptical systems and projection display devices of the present inventionthat use such systems will now be described with reference to FIGS.17-19). More specifically, Embodiments 17 and 18 of the presentinvention, shown in FIGS. 17 and 18, respectively, relate to a firstmode of color separation systems, and Embodiment 19 of the presentinvention, shown in FIG. 19, relates to a second mode of colorseparation systems.

As shown in FIG. 17, the color separation system 4 a of the presentinvention includes: a wavelength-splitting element, which is a dichroicmirror 10 q in FIG. 17, that reflects or transmits portions of anincident light beam according to the wavelength of the light; and apolarization-sensitive beam splitter, which is a reflection-type,polarization sensitive beam splitter 12 m in FIG. 17, that reflects ortransmits an incident light beam according to its direction of linearpolarization and that is arranged adjacent, and at least nearlyparallel, to the wavelength-splitting element.

The color separation systems of the first mode, which include Embodiment17 of the present invention, operate with light beams of differentfirst, second, and third wavelengths but that are incident on the colorseparation systems from the same direction. The color separation systemundertakes color separation of these light beams by emitting the lightbeams of the first and third wavelengths in the same direction withdifferent directions of linear polarization and emitting the light beamof the second wavelength in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.

As shown in FIG. 17, the light beams of all three wavelengths areincident from the right side of the page. The color separation system 4a undertakes color separation of the light beam of the second wavelengthfrom the light beams of the first and third wavelengths. The light beamsof the first and third wavelengths are emitted to the upper side of thepage, and the light beam of the second wavelength is emitted to the leftside of the page. In other words, the dichroic mirror 10 q is set sothat the light beam of the first wavelength is reflected and the lightbeam of the second wavelength is transmitted.

Furthermore, the light beams of the first and second wavelengths thatare incident on the color separation system 4 a are in the secondpolarization state, and the light beam of the third wavelength is in thefirst polarization state. Regarding the light beams that are emittedfrom the color separation system 4 a, the light beam of the firstwavelength is transmitted through and back through the reflective-typepolarization sensitive beam splitter 12 m and emitted in the secondpolarization state. The light beam of the second wavelength istransmitted once through the reflection-type polarization sensitive beamsplitter 12 m and emitted in the second polarization state. The lightbeam of the third wavelength is reflected at the reflection-typepolarization sensitive beam splitter 12 m and emitted in the firstpolarization state. In other words, the reflection-type polarizationsensitive beam splitter 12 m is set so that light beams of the firstpolarization state are reflected and light beams of the secondpolarization state are transmitted.

FIG. 18 is a cross-sectional schematic diagram of a color separationsystem 4 b of Embodiment 18 of the present invention that also relatesto a first mode of the color separation systems. The arrangement ofEmbodiment 18 is clear from FIG. 18 and the description of Embodiment 17above. Therefore, further detailed descriptions are omitted.

The color separation system 4 b is different from the color separationsystem 4 a in the order of the dichroic mirror 10 r and thereflection-type, polarization-sensitive beam splitter 12 n. The dichroicmirror 10 r is also set so that the light beam of the first wavelengthis reflected and the light beams of the second and third wavelengths aretransmitted. However, a similar operation to that of Embodiment 17 isachieved with respect to how the light beams of the first, second andthird wavelengths undergo color separation, and the light beams of thefirst and third wavelengths are emitted in the same direction linearlypolarized in different directions while the light beam of the secondwavelength is emitted in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.Furthermore, the color separation system 4 b is constructed so that thelight beam of the third wavelength is transmitted through and backthrough dichroic mirror 10 r.

The first mode of the color separation systems of the present inventionmay be formed with the minimum number of elements, namely, awavelength-splitting element and a polarization-sensitive beam splitter,with light beams of first, second, and third wavelengths being incidentfrom the same direction.

FIG. 19 is a cross-sectional schematic diagram of a color separationsystem 5 a of Embodiment 19 of the present invention that also relatesto a second mode of the color separation systems. The color separationsystem 5 a of Embodiment 19 includes two wavelength-splitting elements,dichroic mirrors 10 s and 10 t in FIG. 19, that reflect or transmit anincident light beam according to wavelength and at least twopolarization-transforming elements, quarter-wave plates 13 c and 13 d inFIG. 19, that change the direction of linear polarization of incidentlight beams that are arranged adjacent and at least nearly parallel tothe wavelength-splitting elements.

The color separation system of the second mode, Embodiment 19 shown inFIG. 19, is constructed so that when the light beams of the threedifferent first, second, and third wavelengths are incident on the colorseparation system in the same direction, the color separation systemperforms color separation with the light beams of the first and thirdwavelengths being emitted in the same direction with differentdirections of linear polarizations, and the light beam of the secondwavelength being emitted in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.

In FIG. 19, the light beams of the first, second and third wavelengthsare incident from the right side of the page. The color separationsystem 5 a undertakes color separation of the light beam of the secondwavelength from the light beams of the first and third wavelengths sothat the light beams of the first and third wavelengths are emitted tothe upper side of the page and the light beam of the second wavelengthis emitted to the left side of the page. In other words, the dichroicmirror 10 s is set so that the light beams of the first and secondwavelengths are transmitted and the light beam of the third wavelengthis reflected, and the dichroic mirror 10 t transmits the light beam ofthe second wavelength and reflects the light beam of the firstwavelength.

Furthermore, the light beams of the first, second and third wavelengthsthat are incident to the color separation system 5 a are in the firstpolarization state. Regarding the light beams that are emitted from thecolor separation system 5 a, the light beam of the first wavelength istransmitted through and back through the quarter-wave plate 13 c andemitted in the second polarization state. The light beam of the secondwavelength is transmitted once through the quarter-wave plates 13 c and13 d and emitted in the second polarization state. The light beam of thethird wavelength is emitted in the first polarization state with whichit is incident.

The color separation system of the second mode, Embodiment 19 shown inFIG. 19, operates on light beams of the first, second, and thirdwavelengths that are incident from the same direction and linearlypolarized in the same direction.

In addition, the color separation systems of the present inventiondescribed above also have the ability to be used with light pathsreversed from those shown in FIGS. 17-19, as generally taught withregard to optical elements, such as lenses. In other words, thesesystems may be used with light traveling from what is the light emittingside to the light incident side as shown in FIGS. 17-19. In this case,the color separation system functions as a “color synthesis system” withlight beams of the first and third wavelengths being incident from thesame direction with their directions of linear polarization beingdifferent, and light beams of the first, second, and third wavelengthsbeing emitted with the same direction of linear polarization and in thesame direction that the light beam of the second wavelength is incident.

Furthermore, for this case, it is preferred that the light beams emittedfrom the color synthesis systems of the first mode, Embodiments 17 and18, shown in FIGS. 17 and 18, be such that the light beams of the firstand second wavelengths have the same direction of linear polarizationand the light beam of the third wavelength have a different direction oflinear polarization. It is further preferred that the light beamsemitted from the color synthesis systems of the second mode, Embodiment19 shown in FIG. 19, be emitted in the same polarization direction.

Illumination Optical Systems and Projection Display Devices (Embodiments20-24)

The first mode of illumination optical systems and projection displaydevices that use such illumination optical systems of the presentinvention will be described with reference to FIGS. 20-22, that arecross-sectional schematic diagrams of Embodiments 20-22, respectively,of the present invention. These projection-type display devices includeLCOSs 53 a-53 c that display the image information corresponding to thelight beams of the first, second, and third wavelengths, illuminationoptical systems to illuminate these LCOSs 53 a-53 c, and projectionoptical systems for magnified projection of the light beams that haveundergone light modulation by these LCOSs 53 a-53 c. In particular,Embodiment 20 uses the color separation and synthesis system 1 a ofEmbodiment 1 described above, Embodiment 21 uses the color separationand synthesis system 2 c of Embodiment 7 described above, and Embodiment22 uses the color separation and synthesis system 3 a of Embodiment 15described above.

In addition, in FIGS. 20-22, and in FIGS. 23-25 that will be describedlater, the same reference notation is used for elements that have thesame location and similar operation, and reference notations forelements that have similar operation at a different location have thesame numeric components.

The illumination optical systems of FIGS. 20-22 variously include alight source 30, reflectors 31 a and 31 b, integration systems 32 a and32 b, a collimator lens 33 in Embodiment 20, polarization-transformationoptical systems 35 a and 35 b, illumination light beam color separationelements 40 a and 40 b, lenses 41 a-41 j that operate as condensinglenses or relay lenses, polarizing plates 42 a-42 c, a half-wave plate44 a in Embodiment 22, total reflection mirrors 34 a-34 i, colorseparation synthesis systems 1 a, 2 c, 3 a that relate to the presentinvention as described previously, optical path separation elements,which are PBSs, arranged immediately before each of the LCOSs 53 a-53 c,and quarter-wave plates 52 a-52 c.

Furthermore, the projection optical systems of FIGS. 20-22 variouslyinclude the above described optical path separation elements 50 a and 50b and quarter-wave plates 52 a-52 c and further includewavelength-specific, polarization-transforming element 43 a, projectionlight beam synthesis elements 60 a and 60 b, and projection lenses 62a-62 d.

The light source 30 can be a high intensity white light source such asan ultra-high voltage mercury lamp, a metal halide lamp, or similarlight source.

The reflector 31 a or 31 b reflects light from the light source 30 so asto emit the light forward. A concave mirror, such as an ellipsoidalmirror or a parabolic mirror, can be used as the reflector. Thereflector 31 a is an ellipsoidal mirror, and the reflector 31 b is aparabolic mirror.

The integration systems 32 a and 32 b are for adjusting the intensitydistribution of light in a plane perpendicular to the optical axis sothat light beams from the light source can be irradiated efficiently tothe effective aperture of the LCOSs, and a rod integrator or fly-eyelens may be used for these integration systems. Further, various typesof integration systems, such as a stick rod prism that is made of solidglass, a hollow prism where the internal plane is a mirror formed as areflecting coat, a hybrid-type integrator that is a combination of astick rod prism and a hollow prism made by arranging the stick rod prismat the light beam incidence side and arranging the hollow prism at thelight beam emitting side, a polarization-transforming pipe providing thepolarization transformation, or similar devices may be used as rodintegrators. The integration system 32 a indicates a rod integrator, andthe integration system 32 b indicates a fly-eye lens.

The polarization-transforming optical systems 35 a and 35 b transformwhite light emitted from the light source 30 to linearly polarizedlight, and their construction is not limited by the schematicillustration. The combinations of the polarization-sensitive beamsplitters and the quarter-wave plates of Embodiments 20-22separate theilluminating light beams into P polarized light and S polarized lightand then transform the polarization direction of one of these and emitall the light as parallel light beams with the directions of linearpolarization adjusted, which can provide more efficient use of thelight. The polarization-transforming element 35 a emits the illuminationlight beams in the first polarization state, and thepolarization-transforming element 35 b emits the illumination lightbeams in the second polarization state.

The illumination light beam color separation elements 40 a and 40 bperform color separation of illumination light beams of specifiedwavelengths so that light beams of specified wavelengths can besubsequently incident on the color separation and synthesis systems 1 a,2 c, and 3 a from specified directions, and so that specified lightbeams can be variously reflected or transmitted by the color separationand synthesis systems 1 a, 2 c and 3 a. Such wavelength-splittingelements are not limited to a dichroic mirror. For example, a prism maybe used. The illumination light beam color separation element 40 aprovides transmission of light beams of the first and second wavelengthsand reflection of the light beam of the third wavelength, and theillumination light beam color separation element 40 b providesreflection of light beams of the first and second wavelengths andtransmission of the light beam of the third wavelength.

The polarizing plates 42 a-42 f adjust the direction of linearpolarization at arranged locations, near the polarization-transformingelement, before the second dichroic mirror, and before and after thePBS, which helps prevent deterioration in the contrast and brightness ofan image projected on a projection screen. Polarizing plates 42 a-42 c,42 e, and 42 f adjust the polarization direction of light beams of thefirst polarization state, and the polarizing plate 42 d adjusts thepolarization direction of a light beam of the second polarization state.

The half-wave plate 44 a transform the light beam of the thirdwavelength of Embodiment 22 from the second polarization state to thefirst polarization state before it is incident on color separation andsynthesis system 3 a. In the illumination optical systems and theprojection display devices such as Embodiment 22 of the presentinvention, where the construction is such that the polarization statesof the light beams of the first, second, and third wavelengths that areincident on the color separation and synthesis system are different,such as for color separation and synthesis system 3 a of Embodiment 22,it is preferable that the polarization state of all the light beams fromlight source 30 be transformed to a single polarized state by passingtogether through a polarization-transforming optical system and then thepolarized state of one of the desired light beams adjusted again.Therefore, a relay optical system that includes lenses 41 g-41 i isprovided in Embodiment 22 to assist in the proper adjustment of thepolarization state of the light beam of the third wavelength. As shownvariously in FIGS. 20-22, the collimator lens 33 and lenses 41 a-41 jare illustrated schematically, and the composition, such as the numberof lens components and lens elements, may be varied.

The optical path separation element 50 a, which is a PBS, uses the factthat the illumination light beam of the second wavelength becomes aprojection light beam as its linear polarization direction is changedninety degrees by reflection at the LCOS 53 b and transmission back andforth through the quarter-wave plate 52 b so that the optical path isdivided by transmitting one of either the illumination light beam andthe projection light beam by the internal polarization separation filter51 a and by the internal polarization separation filter 51 a reflectingthe other. In Embodiments 20-25 that relate to the present invention,the polarization separation filter 51 a reflects the light beam of thefirst polarization state and transmits the light beam of the secondpolarization state. The illumination light beam is reflected and theprojection light beam is transmitted in Embodiment 20 and Embodiment 21,and the illumination light beam is transmitted and the projection lightbeam is reflected in Embodiment 22. In addition, because generally PBSpolarized light separation filters are more efficient in reflecting Spolarized light than P polarized light, preferably an arrangement whereS polarized light is reflected at the PBS is used.

Furthermore, the optical path separation element 50 b is also a PBS andis used for separating the optical path of the illumination light beamand the projection light beam by the reflecting and transmittingoperation of the internal polarization separation filter 51 b, and theillumination light beams of the first and third wavelengths havedifferent linear polarization directions as they are incident on theoptical path separation element 50 b from the same direction, afterwhich they each irradiate a corresponding one of LCOSs 53 a or 53 c bytransmission or reflection in accordance with their polarizationdirection. The projection light beams that are reflected at each of theLCOSs 53 a and 53 c are incident to the optical path separation element50 b once again, are transmitted or reflected according to thepolarization direction, and then are emitted in the same direction. InEmbodiments 20-25 of the present invention, the polarization separationfilter 51 b reflects light beams of the first polarization state andtransmits light beams of the second polarization state. The illuminationlight beams of the first wavelength and the projection light beams ofthe third wavelength are transmitted, and the projection light beams ofthe first wavelength and the illumination light beams of the thirdwavelength are reflected in Embodiments 20-22.

The wavelength-specific, polarization-transforming element 43 a rotatesthe direction of linear polarization of a light beam by a specifiedangle. The wavelength-specific, polarization-transforming element 43 aof Embodiments 20-22 transforms light beams of the third wavelength fromthe second polarization state to the first polarization state.

The projection light beam synthesis elements 60 a and 60 b synthesizelight beams of the first and third wavelengths that are incident from adifferent direction with light beams of the second wavelength, and emitall the light beams in the same direction. The projection light beamsynthesis element 60 a is a PBS, and the projection light beam synthesiselement 60 b is a dichroic prism. In Embodiments 20 and 21, at theprojection light beam synthesis elements 60 a, which is a PBS, the lightbeams of the first and third wavelengths are incident in the firstpolarization state and are reflected and the light beams of the secondwavelength are incident in the second polarization state and aretransmitted, so that all the light beams are synthesized. Further, atthe projection light beam synthesis element 60 b, which is a dichroicprism in Embodiment 22, the light beams of the first and thirdwavelengths are reflected in order to synthesize the light beams.

The projection lenses 62 a-62 d magnify and project the light beamscontaining the image information of the projection light beams that arereflected at LCOSs 53 a-53 c in order to produce a full color image (notshown in the drawings). As shown in FIGS. 20-22, the entire lens systemsare shown as the projection lenses 62 a-62 d that are variously arrangedin front of and behind the projection light beam synthesis elements 60 aand 60 b. For example, as shown in FIG. 21, the projection lens 62 a andthe projection lens 62 c, or the projection lens 62 b and the projectionlens 62 c comprise a projection lens system.

The illumination optical systems of Embodiments 20-22, in the same wayas the illumination optical system of Japanese Laid-Open PatentPublication 2001-100155 described above, provide two light beams havingdifferent polarization directions and wavelengths to the PBS 50 b thatis arranged adjacent to two LCOSs 53 a and 53 c without using awavelength-specific, polarization-transforming element, which allowslower production costs, as well as preventing deterioration of thecontrast and deterioration of the image formed, which may be associatedwith properties of angle of incidence and wavelength related towavelength-specific, polarization-transforming elements.

Furthermore, in order to compare the prior art to the illuminationoptical systems of Embodiments 20-22, a projection-type display devicethat provides an illumination optical system that is almost the same asthe illumination optical system described in Japanese Laid-Open PatentPublication 2001-100155 is shown in FIG. 28 as prior art Example 3. InFIG. 28, the same reference notation is used for the last two digits ofthe numbers and for the alphabet letters for elements that have asimilar location and similar operation as those of FIGS. 20-22, andotherwise the same reference notation is used for the last two digits ofnumbers for elements that have similar operation at a differentlocation. Regarding FIG. 28, the detailed descriptions of the elementsthat have essentially the same operation at the same location with theelements shown in FIGS. 20-22 are omitted.

In the prior art Example 3 of FIG. 28, the illumination light beamseparation and synthesis system 270 that is arranged in place of thecolor separation and synthesis systems 1 a, 2 c, and 3 a of the presentinvention includes a dichroic mirror that is set so that the light beamof the first wavelength can be reflected and the light beams of thesecond and third wavelengths can be transmitted. By doing this, thelight beams of the first and second wavelengths that are incident fromthe same direction and the light beam of the third wavelength undergocolor separation and color synthesis, and the light beams of the firstand third wavelengths are emitted in the same direction with differentlinear polarization states, and, at the same time, the light beam of thesecond wavelength is emitted in a different direction from the directionin which the light beams of the first and third wavelengths are emitted.

Furthermore, the half-wave plate 244 c transforms the light beam of thethird wavelength from the first polarization state to the secondpolarization state and adjusts the polarization state of the light beamof the third wavelength that is incident on the illumination light beamseparation and synthesis system 270. The polarizing plate 242 l thatfollows and is adjacent the half-wave plate 244 c adjusts thepolarization direction of the light beam of the third wavelength so thatit is emitted in the second polarization state. There are nodescriptions regarding polarizing elements in Japanese Laid-Open PatentPublication 2001-100155. However, at least some polarizing elements,such as polarizing plates 242 b-242 e and 242 l shown in prior artExample 3, are necessary in order to construct a projection displaydevice that produces an image with satisfactory contrast.

Furthermore, the optical path separation system 250 b is a PBS and isarranged for separating the optical paths of the illumination lightbeams and the projection light beams by reflecting and transmittingoperations at the internal polarization separation filter 251 b that ispractically the same as the optical path separation element 50 b, andthe polarization separation filter 251 b reflects the illumination lightbeam of the first wavelength and the projection light beam of the thirdwavelength and transmits the projection light beam of the firstwavelength and the illumination light beam of the third wavelength.

When comparing the illumination optical systems of Embodiment 20-22,shown in FIGS. 20-22, and the illumination optical system of prior artExample 3, shown in FIG. 28, it is evident that it is possible, by usingthe color separation and synthesis systems 1 a, 2 c, and 3 a of thepresent invention, to construct an illumination optical system so thatthe polarization-transforming elements are located at positions wherethey do not cause increases in size, so that the number ofwavelength-specific, polarization-transforming elements can bedecreased, and so that a generally useful polarization element can bearranged adjacent to the incidence side of the polarization-sensitivebeam splitter.

The illumination optical system of Embodiment 20 can be constructed, byusing the color separation and synthesis system 1 a of the presentinvention, so that light beams of the first and second wavelengths areincident in the same direction and with the same linear polarizationdirection and a light beam of the third wavelength having the samelinear polarization direction is incident in a different direction fromthe light beams of the first and second wavelengths, and light beams ofthe first and third wavelengths are emitted in the same direction withdifferent linear polarization states and the light beam of secondwavelength is emitted in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.Therefore, it is not necessary to arrange a polarization-transformingelement for transforming the polarization state of the light beam of thethird wavelength as is done with regard to illumination light beam colorseparation element 240 by half-wave plate 244 c in prior art Example 3.

In addition to simplifying the processes of alignment and adjustment byreducing the number of independently placed optical elements, inresponse to the problem of the half-wave plate 244 c becoming large dueto the light beam diameter being large when placed in close proximity tothe light source 230, the half-wave plate 11 a (FIG. 1) that is includedwithin the color separation and synthesis system 1 a has the ability toprovide a smaller scale and lower cost by being placed farther from thelight source 30. This is true not only for the color separation andsynthesis system 1 a of Embodiment 1, but also is true for theprojection display devices that use the other color separation andsynthesis systems of the first mode of the present invention.

Furthermore, this illumination optical system provides an optical pathwithout a polarization element for adjusting the polarization directionbeing installed between the color separation and synthesis system 1 aand the PBS 50 b.

The illumination optical system of Embodiment 21 can be constructed, byusing the color separation and synthesis system 2 c of the presentinvention, so that light beams of the first and second wavelengths areincident in the same direction and with the same linear polarizationdirection and a light beam of the third wavelength having the samelinear polarization direction is incident in a different direction fromthe light beams of the first and second wavelengths, and light beams ofthe first and third wavelengths are emitted in the same direction withdifferent linear polarization states and the light beam of the secondwavelength is emitted in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.Therefore, it is not necessary to arrange a polarization-transformingelement such as half-wave plate 244 c of prior art Example 3, similar toEmbodiment 20.

Furthermore, it is not necessary to arrange an element in order toadjust the polarization direction as with the polarizing plates 242 b,242 l, and 242 c of prior art Example 3in this illumination opticalsystem using the color separation and synthesis system 2 c of thepresent invention. The polarizing plate 12 c (FIG. 7) is arranged in thecolor separation and synthesis system 2 c as the polarization-sensitivebeam splitter in this illumination optical system, and this polarizingplate 12 c achieves the equivalent role as the three polarizing plates242 b, 242 l, and 242 cof prior art Example 3.

In other words, in the color separation and synthesis system 2 c,polarizing plate 12 c adjusts the polarization direction of the lightbeam that is transformed to the second polarization state at thehalf-wave plate 11 g by passing through the illumination light beamcolor separation element 40 b, which is a dichroic mirror, for the lightbeam of the first wavelength. It adjusts the polarization direction ofthe light beam passing through the illumination light beam colorseparation element 40 b, adjusts a polarization direction of the lightbeam passing through the dichroic mirror 10 g for a light beam of thesecond wavelength, and adjusts the polarization direction of the lightbeam passing through the illumination light beam color separationelement 40 b and the dichroic mirror 10 g for a light beam of the thirdwavelength. Thus, in this illumination optical system, the optical pathbetween the color separation and synthesis system 2 c and the PBS 50 a,as well as the optical path between the color separation and synthesissystem 2 c and the PBS 50 b, do not require a separate polarizingelement for adjusting the polarization direction. Thus, no additionalpolarizing element for adjusting the polarization direction (other thanin the color separation and synthesis system 2 c) is needed in thisillumination optical system.

In addition to simplifying the processes of alignment and adjustment andlowering costs by reducing the number of independently placed opticalelements, the use of the polarizing plate 12 cincluded within the colorseparation and synthesis system 2 c makes a smaller scale and furthercost reduction possible over the use of polarizing plates 242 b and 242l by it being arranged farther from the light source 30. Furthermore,the polarizing plate 12 c enables improvement in contrast and reductionin the deterioration of the polarization properties than with the use ofpolarizing plates 242 b and 242 l by its placement closer to the displayelements.

This is true not only for the color separation and synthesis system 2 cof Embodiment 7, but also is true for the projection display devicesthat use the other color separation and synthesis systems of the secondmode of the present invention.

The illumination optical system of Embodiment 22 can be constructed byusing the color separation and synthesis system 3 a of the presentinvention, so that light beams of the first and second wavelengths areincident in the same direction with the same linear polarizationdirection and a light beam of the third wavelength having a differentlinear polarization direction is incident in a different direction fromthe light beams of the first and second wavelengths, and light beams ofthe first and third wavelengths are emitted in the same direction withdifferent linear polarization states and the light beam of secondwavelength is emitted in a different direction from the direction inwhich the light beams of the first and third wavelengths are emitted.Therefore, it is not necessary to arrange elements for adjusting thepolarization direction as with the polarizing plates 242 b, 242 l, and242 c of prior art Example 3, similar to Embodiment 21. In thisillumination optical system, the polarizing plate 12 k (FIG. 15) isincluded within the color separation and synthesis system 3 a as thepolarization-sensitive beam splitter while also playing a roleequivalent to the three polarizing plates 242 b, 242 l, and 242 c ofprior art Example 3.

In other words, in the color separation and synthesis system 3 a, thesingle polarizing plate 12 k adjusts the linear polarization directionof the light beam passing through the illumination light beam colorseparation element 40 a, which is a dichroic mirror, for a light beam ofthe first wavelength; it adjusts the linear polarization direction ofthe light beam passing through the illumination light beam colorseparation element 40 a and also adjusts the linear polarizationdirection of the light beam passing through the dichroic mirror 10 o forthe light beam of the second wavelength; and it adjusts the linearpolarization direction of the luminous flux passing through the dichroicmirror 10 o for the light beam of the third wavelength. By doing this,this illumination optical system provides an optical path between thecolor separation and synthesis system 3 a and the PBS 50 a, as well asbetween the color separation and synthesis system 3 a and the PBS 50 bwithout the use of a separate polarizing element for adjusting thepolarization direction. That is, a polarizing element for adjusting apolarization direction is installed only in the color separation andsynthesis system 3 a in this illumination optical system.

In addition to simplifying the processes of alignment and adjustment andlowering costs by reducing the number of independently placed opticalelements, the use of the polarizing plate 12 k included within the colorseparation and synthesis system 3 a makes a smaller device possible andmakes possible further cost reduction over the use of polarizing plates242 b and 242 l by it being arranged farther from the light source 30.Furthermore, the polarization plate 12 k enables improvement in contrastand reduction in the deterioration of the polarization properties thanwith the use of polarizing plates 242 b and 242 l by its placementcloser to the display elements. This is true not only for the colorseparation and synthesis system 3 a of Embodiment 15, but also is truefor the projection display devices that use the other color separationand synthesis systems of the second mode of the present invention.

The second mode of the illumination optical system and the projectiondisplay device using it of the present invention are shown in thecross-sectional schematic diagrams of FIGS. 23 and 24, which showEmbodiments 23 and 24 of the present invention, respectively. Theseembodiments use color separation systems of the present invention inillumination optical systems of the present invention. Embodiment 23uses the color separation system 4 a that relates to the above describedEmbodiment 17, and Embodiment 24 uses the color separation system 5 athat relates to the above described Embodiment 19. These projectiondisplay devices include, similarly to the illumination optical systemsand the projection display devices of Embodiments 20-22: LCOSs 53 a-53 cthat are display elements that display image information correspondingto the light beams of the first, second, and third wavelengths; anillumination optical system to illuminate these LCOSs 53 a-53 c; and aprojection optical system to magnify and project the light beams thatundergo light modulation by these LCOSs 53 a-53 c. Regarding FIG. 23 andFIG. 24, detailed descriptions are omitted for the optical elements thathave essentially the same operation at the same location as the devicesshown in FIGS. 20-22.

These illumination optical systems include a light source 30, reflector31 b, integration system 32 b, polarization-transformation opticalsystems 35 a and 35 b, lenses 41 c and 41 k operating as a condensinglens system, wavelength-specific, polarization-transforming element 43 b(Embodiment 23), and polarizing plates 42 g and 42 h (Embodiment 24).Additionally, color separation systems 4 a and 5 a that relate to thepresent invention are provided appropriately, as are optical pathseparation elements 50 a and 50 b, each of which is a PBS arranged asshown before the LCOSs 53 a-53 c, and quarter-wave plates 52 a-52 c.

Furthermore, the projection optical systems include the previouslymentioned optical separation elements 50 a and 50 b, the quarter-waveplates 52 a-52 c, polarizing plates 42 e, 42 f, and 42 i, thewavelength-specific, polarization-transforming elements 43 a and 43 c,the projection light synthesis element 60 b, and the projection lens 62d.

The wavelength-specific, polarization-transforming element 43 btransforms the light beam of the third wavelength from the secondpolarization state to the first polarization state in the illuminationoptical system of Embodiment 23. This determines the polarization stateof the light beam of the third wavelength, among the light beams of thefirst, second, and third wavelengths, as it is incident on the colorseparation system 4 a in the same direction but in a differentpolarization state than the light beams of the first and secondwavelengths. Similarly, the wavelength-specific,polarization-transforming element 43 c transforms the light beam of thefirst wavelength from the first polarization state to the secondpolarization state in the projection optical system of Embodiment 24.

The polarizing plates 42 e-42 g adjust the linear polarization directionof light beams in the first polarization state and the polarizing plates42 h and 42 i adjust the linear polarization direction of the lightbeams in the second polarization state. The lenses 41 c and 41 k areshown schematically, and their construction, as well as the number oflenses, may be modified appropriately.

The optical path separation element 50 a transmits the illuminationlight beam of the second wavelength in Embodiment 23 and Embodiment 24and reflects the projection light beam. Furthermore, the optical pathseparation element 50 b transmits the illumination light beam of thefirst wavelength and the projection light beam of the third wavelengthin Embodiment 23 and Embodiment 24 and reflects the projection lightbeam of the first wavelength and the illumination light beam of thethird wavelength.

The projection light beam synthesis element 60 b is a dichroic prism,the light beams of the first and third wavelengths are reflected inEmbodiment 23, and the light beam of the second wavelength istransmitted and synthesized. Furthermore, the light beams of the firstand third wavelengths are transmitted in Embodiment 24, and the lightbeam of the second wavelength is reflected and synthesized.

As a representative example of color separation systems of the presentinvention, the illumination optical systems of Embodiment 23 andEmbodiment 24 increase the choices of the arranging positions of theoptical members more than those shown in Embodiments 20-22by using thecolor separation systems 4 a and 5 a of the present invention in theseoptical systems, and thereby the degree of freedom in the design ofvarious optical systems of the present invention are increased. Thecolor separation systems 4 a and 5 a are designed to achieve anoperation that undertakes color separation of the light beams of first,second, and third wavelengths that are incident from the same direction,the light beams of the first and third wavelengths are emitted in thesame direction with different directions of linear polarization, and thelight beam of the second wavelength is emitted in a different directionfrom the direction in which the light beams of the first and thirdwavelengths are emitted. Therefore, a more simple and compactarrangement from the light source 30 to the color separation systems 4 aand 5 a than that shown in Embodiment 20- Embodiment 22 may be achieved.

The illumination optical system of Embodiment 23, by using the colorseparation and synthesis system 3 a of the present invention, isconstructed so that light beams of the first and second wavelengths withthe same linear polarization direction and a light beam of the thirdwavelength having a different linear polarization direction are allincident in the same direction, and light beams of the first and thirdwavelengths are emitted in the same direction with different linearpolarization states and the light beam of second wavelength is emittedin a different direction from the direction in which the light beams ofthe first and third wavelengths are emitted. Therefore, it is notnecessary to arrange polarizing elements separate from thepolarization-transforming element. By decreasing the number of separateoptical elements, lower costs and simplified alignment of the opticalelements can be achieved. In the illumination optical system ofEmbodiment 23, the polarization-sensitive beam splitter 12 m is arrangedwithin the color separation system 4 a (FIG. 17) and acts as apolarizing plate as well as a polarization-sensitive beam splitter sothat this polarization-sensitive beam splitter 12 m plays a roleequivalent to a plurality of polarizing plates.

In other words, the color separation system 4 a is constructed so thatthe single polarization-sensitive beam splitter 12 m can adjust thepolarization direction of the light beam of the first wavelength passingthrough the dichroic mirror 10 q, can adjust the polarization directionby transmitting the light beam of the second wavelength, and can adjustthe polarization direction of the light beam of the third wavelengththat is transformed to the first polarization state at thewavelength-specific, polarization-transforming element 43 b. By doingthis, in this illumination optical system, an optical path between thecolor separation system 4 a and the PBS 50 a, as well as the colorseparation system 4 a and the PBS 50 b, does not need to include apolarizing element for adjusting a polarization direction. Rather, thepolarizing element for adjusting a polarization direction is installedonly in the color separation system 4 a in this illumination opticalsystem.

The single polarization-sensitive beam splitter 12 m included within thecolor separation and synthesis system 4 a is arranged relatively farfrom the light source 30, and this makes possible miniaturization andlower cost. Further, the polarization-sensitive beam splitter 12 m isarranged comparatively near to the display elements, and this makespossible improvement in the contrast of a projected image whiledecreasing the deterioration of the polarization properties.Furthermore, contrast can be improved even if the polarization-sensitivebeam splitter 12 m is the only polarizing plate included within theillumination optical system because the light is used so efficiently.

This is true not only for the color separation and synthesis system 4 aof Embodiment 17, but also is true for the projection display devicesthat use the other color separation and synthesis systems of the firstmode of the present invention.

In the illumination optical system of Embodiment 24, by using the colorseparation and synthesis system 5 a of the present invention, the lightbeams of the first, second and third wavelengths with the same linearpolarization direction are all incident from the same direction, and thelight beams of the first and third wavelengths are emitted in the samedirection with different linear polarization states, and the light beamof second wavelength is emitted in a different direction from thedirection in which the light beams of the first and third wavelengthsare emitted. Therefore, it is not necessary to arrange thewavelength-specific, polarization-transforming element 43 b before thecolor separation system 5 a as in Embodiment 23, which avoids reducedcontrast in a projected image and deterioration of imaging performance,while at the same time lowers production costs. By decreasing the numberof separate optical elements, lower cost and simplified alignment can beachieved. In this illumination optical system, the optical paths betweenthe color separation system 5 a and the PBS 50 a, as well as the colorseparation system 5 a and the PBS 50 b, do not need to include apolarizing element for adjusting the polarization direction. This istrue not only for the color separation system 5 a of Embodiment 19, butalso is true for the projection display devices that use the other colorseparation systems of the second mode of the present invention.

Projection Optical Systems And Projection Display Devices (Embodiment25)

A mode of projection optical systems and projection display devicesusing embodiments of the present invention will be described below withreference to FIG. 25 that schematically shows Embodiment 25 thatincludes a projection optical system and projection display device ofthe present invention. This device uses a color synthesis system 4 a′ ofthe present invention as one part of the projection optical system.Additionally this device uses the color separation system 5 a of thepresent invention as one part of the illumination optical system.

This projection display device includes, similar to the projectiondisplay devices of Embodiments 20-24, the LCOSs 53 a-53 c that aredisplay elements to display the image information corresponding to thelight beams of the first, second, and third wavelengths, an illuminationoptical system to illuminate these LCOSs 53 a-53 c, and a projectionoptical system to magnify and project the light beams that have beenmodulated with image information by these LCOSs 53 a-53 c. RegardingFIG. 25, the detailed descriptions are omitted for those opticalelements having essentially the same operation at the same location asthe devices shown in FIGS. 20-24.

The illumination optical system includes a light source 30, a reflector31 b, an integration system 32 b, a polarization-transformation opticalsystem 35 b, lenses 41 c and 41 k that operate as a condensing lenssystem, polarizing plates 42 j and 42 k, and a color separation system 5a that relates to the present invention, and further includes theoptical path separation elements 50 a and 50 b, which are PBSs, arrangedimmediately before each of the LCOSs 53 a-53 c, and the quarter-waveplates 52 a-52 c.

This illumination optical system is of nearly the same construction asthat shown in Embodiment 24 that provides the color separation system 5a. However, the polarization state of each light beam is switched fromthe first polarization state to the second polarization state in FIG.25. This illumination optical system includes apolarization-transformation optical system 35 b that emits theillumination light beams in the second polarization state, a polarizingplate 42 j for adjusting the polarization direction of the light beamsin the second polarization state, and a polarizing plate 42 k foradjusting the polarization direction of the light beam in the firstpolarization state. Further, the optical path separation element 50 areflects the illumination light beam of the second wavelength andtransmits it as a projection light beam. Furthermore, the optical pathseparation element 50 b reflects the projection light beam of the thirdwavelength and the illumination light beam of the first wavelength andtransmits the projection light beam of the first wavelength and theillumination light beam of the third wavelength.

The projection optical system includes the previously mentioned opticalpath separation elements 50 a and 50 b, quarter wave-plates 52 a-52 c,and further includes a color synthesis system 4 a′ for synthesizing theprojection light beams, as well as projection lens 62 d.

The color synthesis system 4 a′ of Embodiment 25 arranges the colorseparation system 4 a shown in FIG. 17 so that light can proceed fromthe light emitting side of the color separation system 4 a to the lightincidence side. In other words, the color synthesis system 4 a′ isarranged to operate so that the light beam of the first wavelength inthe second polarization state, as well as the light beam of the thirdwavelength in the first polarization state, that are incident from thebottom side of the page as shown in FIG. 25 and the light beam of thesecond wavelength that is incident from the right side of the page areall emitted in the same direction to the left side of the page. Thecolor synthesis system 4 a′, in this manner, synthesizes all three lightbeams that have undergone light modulation by the LCOSs 53 a-53 c to beone light beam that is emitted in a single direction, which is towardsthe projection lens 62 d. In the present Embodiment, because the colorsynthesis system 4 a′ is formed as a prism with its incidence plane andits emitting plane perpendicular to the optical axis of the projectionoptical system, and because the dichroic mirror 10 q and thereflection-type, polarization-sensitive beam splitter 12 m are arrangedadjacent and at least nearly parallel within this prism, the aberrationcorrection is satisfactory and the amount of light that is lost is verylow.

As described above, the dichroic mirror 10 q is set so that the lightbeam of the first wavelength is reflected and the light beam of thesecond wavelength is transmitted, and the reflection-type,polarization-sensitive beam splitter 12 m is set so that the light beamof the first polarization state is reflected and the light beam of thesecond wavelength is transmitted. Regarding the light beam that isincident on the color synthesis system 4 a′, the light beam of the firstwavelength is transmitted through the reflection-type,polarization-sensitive beam splitter 12 m, reflected at the dichroicmirror 10 q, transmitted through the reflection-type,polarization-sensitive beam splitter 12 m once again, and then emittedin the second polarization state. The light beam of the secondwavelength is transmitted through the dichroic mirror 10 q and thereflection-type, polarization-sensitive beam splitter 12 m, and thenemitted in the second polarization state. The light beam of the thirdwavelength is reflected at the reflection-type, polarization-sensitivebeam splitter 12 m and emitted in the first polarization state.

As is evident from the projection optical system of Embodiment 25 usingthe color synthesis system 4 a′, according to the projection opticalsystem using the color synthesis system of the present invention, it isnot necessary to arrange a wavelength-specific,polarization-transforming element or a polarizing element in order toadjust the polarization direction of the light beam either between theoptical path separation element 50 a and the color synthesis system 4 a′or between the optical path separation element 50 b and the colorsynthesis system 4 a′, which is different from Embodiments 20-24. In theprojection optical system of Embodiment 25, because thepolarization-sensitive beam splitter 12 m is arranged within the colorsynthesis system 4 a′ as a polarization-sensitive beam splitter, thepolarization direction can be adjusted at a position that follows thepolarization-sensitive beam stage of the optical path separationelements 50 a and 50 b, which are PBSs, for the light beams of the firstand third wavelengths. In addition to simplifying alignment and loweringcost by reducing the number of polarizing plates, devising thesimplification of the alignment adjustment process and the low cost bythe reduction of the polarizing plates, an improvement to the contrastand brightness can be achieved. Further, because it is not necessary touse the wavelength-specific, polarization-transforming element that maynot necessarily be satisfactory in wavelength properties and incidenceangle properties, in addition to the lowering of costs, deterioration ofthe imaging performance can be prevented and reduction in contrastfurther prevented.

The projection-type display device of Embodiment 25 uses the colorseparation system 5 a and the color synthesis system 4 a′ of the presentinvention in the illumination optical system and the projection opticalsystem, respectively. Similar effects can be expected when other colorseparation and synthesis systems or color separation systems of thepresent invention are used in the illumination optical system, and whenother color synthesis systems that relate to the present invention areused in a projection display device that uses a projection opticalsystem.

The color separation and synthesis systems, the color separationsystems, as well as the color synthesis systems of the presentinvention, and the illumination optical systems, the projection opticalsystems and the projection display devices of the present invention thatuse the color separation and synthesis systems, the color separationsystems, and the color synthesis systems of the present invention arenot limited to the embodiments described above, but may be modified invarious ways. For instance, the color separation and synthesis systems,the color separation systems, and the color synthesis systems may notonly variously use a dichroic mirror and dichroic prism, but may use ahologram, for example, as a wavelength-splitting element. In addition,various manufacturing methods may be used to make various elements, forexample, layers that may be laminated are not limited to being formed byvapor deposition or sputtering techniques as other laminating or coatingtechniques may be used. Also, crystals may be used that achieve the sameoptical effects. Furthermore, in the color separation and synthesissystems, the color separation systems, and the color synthesis systems,a polarization-transforming element is not limited to a half-wave plateor a quarter-wave plate, as variously shown in the embodiments describedabove, but any element that changes the polarization direction of alight beam may be used. Also, a plurality of polarization-transformingelements may be used in one system to achieve the same effects as asingle polarization-transforming element as shown in the embodimentsdescribed above. Additionally, in the color separation and synthesissystems, the color separation systems, and the color synthesis systems,a polarization-sensitive beam splitter is not limited to areflection-type, polarization-sensitive beam splitter. Furthermore, thecolor separation and synthesis systems, the color separation systems,and the color synthesis systems are not limited to the embodimentsdescribed above, but the color separation and synthesis systems, thecolor separation systems, and the color synthesis systems can be freelyvaried by considering the polarization states and wavelengths of thelight beams. For the construction of the illumination optical systems,the projection optical systems, and the projection display devices, atleast one of the color separation and synthesis systems, the colorseparation systems, and the color synthesis systems of the presentinvention may be provided, but they are not limited otherwise in theirconstruction.

In order to make the color reproducibility of the projected imagesatisfactory in a projection display device, a method of arranging anoptical element that decreases the light intensity of a light beam of aspecified wavelength is known. For instance, in the spectraldistribution of wavelength in the visible region of anextra-high-pressure mercury lamp, the red wavelength component withinthe three primary color lights is less in intensity than the othercomponents, and, on the other hand, a peak of light intensity occurs inthe yellow wavelength region. Therefore, using this light source, thecolor picture image as a whole is tinged with a yellowish color.Accordingly, illumination may be performed by decreasing the lightintensity of light in the wavelength region in the vicinity of 580 nmfor the light emitted from the light source. The illumination opticalsystem of the present invention can also make the color reproducibilitysatisfactory through arranging an optical element which decreases thelight intensity of a specified wavelength component for at least one ofthe optical paths within the luminous fluxes which are incident on colorseparation and synthesis systems or color separation systems of thepresent invention as well as the light beams that are emitted from colorseparation and synthesis systems or color separation systems of thepresent invention. In addition, “decreasing the light intensity,” asdescribed above, includes reducing the light intensity of a certainwavelength or wavelength region to zero.

In addition, the color separation and synthesis systems, colorseparation systems, and color synthesis systems of the present inventionare not limited to those where light beams of three differentwavelengths are used. Systems where two or four or more light beams ofdifferent wavelengths are used may be included in the present inventionand such systems may variously provide additional degrees of freedom inthe design of the optical systems of the present invention.

Furthermore, the color separation and synthesis systems, colorseparation systems, and color synthesis systems of the present inventionare not limited to constructions where the light beams are incident fromtwo different directions or from the same direction. For instance,systems where the light beams are incident from three or more differentdirections may be possible, and such systems may variously provideadditional degrees of freedom in the design of the optical systems ofthe present invention.

The present invention is not limited to the aforementioned embodiments,nor to the variations described above, as it will be obvious thatvarious alternative implementations are possible. All such variationsare not to be regarded as a departure from the spirit and scope of theinvention. Rather, the scope of the invention shall be defined as setforth in the following claims and their legal equivalents. All suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A color separation and/or synthesis system for receiving at least twoincident light beams whose wavelengths are different from each other,comprising: a wavelength-splitting element that reflects light of onewavelength and transmits light of another wavelength; apolarization-transforming element that changes the direction ofpolarization of linearly polarized light of one wavelength and that isarranged adjacent and at least nearly parallel to thewavelength-splitting element; and a polarization-sensitive beam splitterthat reflects light having one direction of linear polarization andtransmits light having another direction of linear polarization; whereinthe polarization-sensitive beam splitter is arranged adjacent and atleast nearly parallel to the wavelength-splitting element; and the colorseparation and/or synthesis system operates on two linearly polarizedlight beams of different wavelengths that are incident on the colorseparation and synthesis system so that one of the linearly polarizedlight beams is emitted from the color separation and/or synthesis systemlinearly polarized in a direction that is different than its directionof polarization upon incidence on the color separation and/or synthesissystem, and so that one of the linearly polarized beams is emitted fromthe color separation and/or synthesis system in a different directionthan its direction of propagation upon incidence on the color separationand/or synthesis system.
 2. A color separation and synthesis system forreceiving incident light from different directions and emitting light indifferent directions, comprising: a wavelength-splitting element thatreflects light of one wavelength and transmits light of anotherwavelength; a polarization-transforming element that changes thedirection of polarization of linearly polarized light of one wavelengthand that is arranged adjacent and at least nearly parallel to thewavelength-splitting element; and a polarization-sensitive beam splitterthat reflects light having one direction of linear polarization andtransmits light having another direction of linear polarization; whereinthe polarization-sensitive beam splitter is arranged adjacent and atleast nearly parallel to the wavelength-splitting element; and the colorseparation and synthesis system operates on first and second linearlypolarized light beams of different wavelengths that are incident on thecolor separation and synthesis system from one direction and operates ona third linearly polarized beam of a wavelength different from each ofsaid first and second linearly polarized light beams and that isincident on the color separation and synthesis system from anotherdirection so that the first and third linearly polarized light beams areemitted from the color separation and synthesis system in the samedirection but with directions of linear polarization that are differentfrom one another, and the second linearly polarized light beam isemitted from the color separation and synthesis system in a directionthat is different from said same direction.
 3. The color separation andsynthesis system of claim 2, wherein the three light beams of differentwavelengths are incident on the color separation and synthesis systemwith the same direction of linear polarization.
 4. The color separationand synthesis system of claim 2, wherein at least one of the three lightbeams passes twice through the polatization-transforming element.
 5. Thecolor separation and synthesis system of claim 3, wherein at least oneof the three light beams passes twice through thepolarization-transforming element.
 6. The color separation and synthesissystem of claim 2, wherein at least two of the three light beams thatare incident on the color separation and synthesis system fromdirections that are different pass through the polarization-transformingelement at least once.
 7. The color separation and synthesis system ofclaim 3, wherein at least two of the three light beams that are incidenton the color separation and synthesis system from directions that aredifferent pass through the polarization-transforming element at leastonce.